The present invention relates to pintle-type valves; more particularly, to such valves for variably regulating the flow of fluids, and especially gases, among three ports; and most particularly, to a control valve assembly for controllably varying the flow of gas from one inlet port into two outlet ports (three-way valve), such as may be required for reformate flow control in fuel cell applications.
Pintle-type valves are well known in the art for variably controlling flow of fluids, including gases. The advent of fuel cells as alternative propulsion systems or auxiliary power units for automotive and other similar applications, has created a need for improved, highly specialized gas flow control valves. Such fuel cells are known to use hydrogen gas as an energetic fuel for exothermic combination with oxygen at high temperature. Hydrogen may be supplied continuously to a fuel cell as a xe2x80x9creformatexe2x80x9d product of catalytic degradation of hydrocarbons such as gasoline or methanol. At startup of the reformer, however, the reformer operating temperature typically is too low for production of a satisfactory percentage of hydrogen in the reformate. Therefore, until the reformer achieves a sufficiently high temperature, the fuel cell cannot be started and the reformate output is diverted to a waste burner rather than being simply discharged to the atmosphere. As the percentage of hydrogen in the reformate increases, the reformate output stream is gradually diverted by a three-way valve away from the burner and to the fuel cell. Sensitive control of such diversion is highly important to satisfactory operation of the fuel cell.
The requirements of such valves, including material properties, operating at very high temperatures (800xc2x0 C. or greater), operating in corrosive environments, and minimum tolerance for leakage, are difficult or impossible for prior art valves to meet. Degradation of materials resulting from sustained exposure to such conditions can diminish valve performance significantly, leading ultimately to valve and fuel cell failure. Some components of prior art valves, such as force-balancing springs, may experience appreciable set or relaxation at high temperatures, rendering them useless, or their working lifetimes may be significantly shortened. Operating at such high temperatures can cause excessive linear expansion in critical elements, rendering gas metering inaccurate or impossible. Plastic parts can melt or become deformed, thereby rendering the valve permanently inoperative.
Some prior art specialized industrial gas control valves may meet some of the individual requirements, such as leakage, flow capacity, or operating temperature. However, they are impractical for automotive applications because of excessive size, prohibitive cost, slow response, and required actuation force. The cost of some prior art valves can approach or exceed the targeted cost of the entire vehicle for which a flow-control valve is intended. For these reasons, prior art valves are not suitable.
What is needed is a three-way gas flow control valve assembly having valving components which can stand extremely high operating temperatures (greater than 800xc2x0 C.), actuating components which can operate in moderately high temperatures (100-150xc2x0 C.), and means for thermally isolating the valving components from the actuating components. Such a valve assembly must be relatively small and lightweight, inexpensive to manufacture, highly reliable, and virtually leak-proof.
It is the primary object of the invention to provide an improved three-way valve assembly meeting these criteria for use in selectively controlling the flow of reformate from a hydrocarbon reformer to a waste burner and to a fuel cell.
The invention is directed to a three-way gas control valve assembly for selectively controlling gas flow from one inlet conduit into two outlet conduits or vice-versa, such as may be required for flow control of reformate in fuel cell applications. The valve assembly comprises three subassemblies: a metering subassembly disposable within the high-temperature environment in the fuel cell for mechanically regulating reformate flow; an actuating subassembly disposable outside the fuel cell and connectable to the metering subassembly for actuating a pintle shaft and valve head in the metering subassembly; and a coupling tube subassembly extending through an insulative zone to mechanically couple and thermally isolate the metering and actuating subassemblies.
The metering subassembly comprises a valve body having first and second chambers. The first chamber is provided with first and second opposed valve seats surrounding opposed first and second regulated ports. The first regulated port leads outside the valve, and the second regulated port leads to the second chamber. A dual-faced valve head disposed in the first chamber between the opposed valve seats is connected to a pintle shaft extending through the second regulated port by which the valve head can be axially translated to selectively occlude either the first or second seat but not both simultaneously. The first chamber is provided with a first non-regulating port and the second chamber is provided with a second non-regulating port, each non regulating port leading outside the valve to serve as either a gas inlet or gas outlet to the first and second chambers, respectively.
The actuating subassembly comprises a solenoid actuator having an internal armature and armature shaft for engaging the outer end of the pintle extending through an inner bearing disposed in a wall of the metering subassembly. Armature travel is controlled by computer and an axial position sensor attached to the armature.
The coupling tube subassembly comprises a cylindrical element which surrounds the pintle shaft where it extends through the insulative covering of the fuel cell, supports an outer bearing for the pintle shaft, and connects the valve body to the actuator.